Free piston engine



May 4, i937. H. JNlcKE 2,079,289

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FREE PISTON ENGINE Filed July 24, 1934 s sheets-sheet s dlbYl IIIIIIIIIIIIIIIIIII l'lllla Inventor:

f6 mm Patent-ed May 4, 1937 `ultimo STATES l 2,079,289 FREE Prs'roN ENGINE Hermann Jnicke, Dessau, Germany, :asignar to Hugo Junkers, Munich, Germany; Junkers, ne Bennhold, Hugo Junkers, deceased ThereseI adminlstratrix of uid Application July 24, 1934, Serial No. 736,705 En Germany July 31, 1933 i9 claims.

My invention 'relates to free piston engines, more particularly of the kind in which a pair of free pistons is arranged in a cylinder for reciprocation in opposite direction.

gines of this kind in such manner that the overall length of the engine is considerably reduced. l In a free piston engine with a definite shape and arrangement of the parts the total length is proportional to the stroke of the pistons and amounts to a definite multiple thereof. The stroke ofthe pistons is determined by the stroke volume required for the output of the engine in view of an emcient ratio of the length of the stroke space to the inner diameter of the cylinder. In cylindrical combustion chambers an eicient ratio is obtained if the length of the stroke space is a multiple, for instance the threefold to fourfold of the diameter. In consequence thereof in free piston engines and more particularly in engines having a large` output and requiring a considerable stroke of the pistons, the total length is considerable. the pistons further involves the drawback that the period of oscillation is increased, thereby reducing the number of strokes per unit of time.

My invention allows considerably reducing the length of the stroke of the pistons and thereby also the overall length of the engine, and increasing the number of strokes per unit of time, while maintaining a suitable and eiicient ratio olf llength to inner width thus establishing advantageous conditions of scavenging and of fuel distribution in the charge. By increasing the numr of strokes all dimensions of the engine are reduced at a predetermined output, thus further reducing the overall length of the engine.

In order to reduce the length of stroke of the pistons I provide an annular working space for the pistons, the inner diameter being at least one third of the outer diameter. The inner wall of the working space may be formed by a stationary cylinder or by a cylindrical vextension of one of the pistons, the extension being guided in a gastight manner in a hollow extension provided in the other piston.

In the drawings aixed to this specification and forming part thereof some embodiments of my invention are illustrated diagrammatically by 50 way of example.

In the drawings Fig. 1 is a diagram of one half on an annular working space and Fig. 2 is a similar illustration of one half oi an ordinary cylindrical working space, both iig- It is an object of my invention to improve en- A long stroke of (CL 12S-46) ures serving merely to explain the gist of nrv invention.

Fig. 3 is a sectional view of a free piston engine -accordlng to my invention.'

. Fig. 3a being a side elevation oi a coupling gearing formingJ part of the engine shown in Fis. v

Figs. are sectional views of other embodiments,

Fig. 8 being a transverse section on the line VIII-VIIIofFig.7.

Figs. 9 and 10 are sectional views of other embodiments ofthe invention oi a type similar to that shown in Fig. 4.

In all iigures similar parts are marked with the same reference numerals.

Referring to the drawings and rst to Figs..1 and 2, the working space or combustion chamber shown in Fig. l is annular in shape d and D being the inner and outer diameters, respectively, while s is the length of the chamber. The inner width tothe annular space is equal to 'The cylindrical working space or combustion chamber shown in Fig. 2 has the length si and the diameter D1. Be it assumed that the combustion chambers shown in Figs. l and 2 have equal volumes and equal ratlos of length to inner width'or diameter amounting to 4:1. Hence and 81:41h.

Let us further assume that D=2, d=1, so that s=2. Since the volumes of the combustion chambers are equal, it follows that In making the combustion chamber annular, a space is rendered available in the cylinder forming the inner wall of the combustion chamber, which may advantageously be used in the operation of the engine. for instance as a chamber for scavenging air or exhaust gas, as a liquid tank, as the working chamber of a scavenging pump, as an energy storing device, as a compressor chamber or the like. If desired, however. auxiliary devices such as gearings coupling the free pistons' Witl each other may be arranged in the ,inner cylinder, thus further reducing the space required by the engine. Embodiments of engines of this kindare shown in Figs. 3-7 which stroke volume.

will be described more fully hereinafter.

The annular combustion chamber according to my invention further involves advantages in scavenging by providing scavenging and, if desired, exhaust ports in the inner as well as in the outer cylindrical Wall of the combustion chamber. With the ports arranged in this manner the exhaust gases are more thoroughly removed, this effect being improved by the fact that the exhaust gases are allowed to extend farther into the working chamber. If scavenging ports only are provided in each wall, the exhaust ports being provided merely in one of the Walls, the scavenging ports will be shorter than usual, while the exhaust ports have the usual length. Thus for the expansion of the exhaust gases a greater portion of the stroke, viz. the portion between the beginning of the opening ofthe exhaust ports and the beginning of the opening of the scavenging ports and in consequence thereof a longer period of time is available. If exhaust ports are also provided in each Wall, the length of these exhaust ports ls also reduced, so that no saving of time is obtained, but the total crosssection of the exhaust ports is increased, thus facilitating the expansion of the exhaust gases.

By shortening the exhaust ports the portion of the stroke volume not available for delivering energy, which corresponds to the length of the exhaust ports, is reduced with respect to the total Thus while maintaining the eilicient stroke volume and the output of the engine, the total stroke of each piston is reduced by this reduction of the exhaust ports, the overall length of the engine being reduced by a multiple of this value, or, while maintaining the total stroke, the efficient stroke volume and thereby also the output of the engine may be increased. Y

The scavenging ports may be inclined to the radial direction, preferably in such manner that the currents of scavenging air entering the combustion chamber through the inner ports as well as through the outer ones carry out circulating movements of uniform direction, if possible at equal speed, so that they unite in a uniform circulating current of scavenging air.

In Fig. 3 I is the outer cylinder forming the outer Wall of the combustion chamber, 2 and 3 are compression cylinders having a larger diameter than cylinder I and forming extensions thereof. 4 and 5 are the end walls of the engine, to which the inner cylinder 6 extending over the total length of the engine is secured. The iliying bodies are formed by the motor pistons 1, 8, the connecting members 9, I6 and the compressor pistons II, I2, respectively. The outer cylinder I and the inner cylinder 6 enclose the annular working space or combustion chamber I3, the compressor chambers I4 and I5 being arranged at the ends of the engine and provided with suction valves I6 and pressure valves I1.

I8, I9 are delivery pipes, throughv which the compressed gas or air produced in the engine is withdrawn. The spaces 20 and 2l existing between the combustion chamber I3 and the compression chambers I4 and I5, respectively, are designed as scavenging pump chambers and are provided with suction valves 22 and pressure valves 23. 24 is a pipe connecting the pressure valves 23 to the inner left hand space 25 of the inner cylinder 6 operating as a container for scavenging air being connected to the combustion chamber by means of scavenging ports 21. The right hand portion 28 of the inner cylinder 6, which is separated from the left hand portion by a partition 26, is designed as an exhaust chamber connected to the combustion chamber I3 by exhaust ports 29 and leading the exhaust gases to the exhaust pipe 30. In order to obtain an accurately symmetrical reciprocation of the pistons, a gearing is provided comprising racks 3l and 32 connected to the compressor pistons II and I2, respectively, which engage a pinion 33 arranged for rotation about a stationary shaft. As will be seen from Fig. 3, two gearings of this kind are provided, one on each side of the engine, the other gearing being marked by the reference numerals 3|', 32', 33.

The operation of the engine is the same as that of the usual free piston engine and need not be described in detail. Fuel is delivered to the combustion chamber I3 by a suitable delivery nozzle or the like (not shown) and mixed with air. The charge is ignited, the pistons being driven apart. When the pistons approach their outer dead centre positions, the exhaust ports 29 and shortly thereafter the scavenging ports 21 are uncovered, so that the exhaust gases are withdrawn from the combustion chamber and scavenging air is supplied by the scavenging pump formed by the chambers 20 and 2|. During the outward stroke of the pistons air is compressed in the combustion chambers I4 and I5, the compressed air being withdrawn through the pipes I8 and I9, except the air filling the dead volumes of the chambers I5 and I6, which will expand again and return the pistons into their inner dead centre positions, so that the cycle of operations can be repeated. It should be understood, that by designing the combustion chamber and the pistons in the manner above described the overall length of the engine is considerably reduced.

In the modified embodiment shown in Fig. 4 the diameters of the compressor pistons II and I2 and of the working pistons 'I and 8 are equal. In order to obtain a suicient working surface of the compressor pistons, the length of the inner cylinder 6 is reduced so as to extend only substantially along the stroke of the motor pistons I and 8, respectively, supporting rods 34, 35 being provided'within the range of the stroke of the compressor pistons II and I2, which extend through suitable perforations of the pistons II and I2, respectively. In order to obtain a suiicient amount of scavenging air, a partition 36 is provided in the right hand portion of the engine between the motor piston 8 and the compressor piston I2, which is packed with regard to the connectingmember I0, two. chambers 3'I and 38, being thus formed, chamber 31 being connected to atmosphere by a port 39 formed in the outer cylinder, While the other chamber 38 forms the scavenging pump chamber together with the chamber 2| enclosed by the connecting member I0. 43 is a port formed in the wall of the connecting member I0 and connecting the chambers 2I and 38 with each other, the suction valve 22 and the pressure valve 2.3 of the scavenging pump being arranged in the manner indicated in Fig. 4. At the left hand portion of the engi/ne the chamber 20 enclosed by the connectingv member 9 is chamber is constituted by the difference of the Cir Cil

cross-sections of the cylinder 6 and the supporting rod 34. If desired, the chamber 31 provided at the right hand portion of the engine may be used as an operating chamber, for instance as an energy storing chamber, an additional compressor chamber, or a scavenging pump chamber. The chamber 31 may for instance be used as a second compressor stage. The gearing 3|, 32, 33 coupling the nying bodies with each other is arranged in the inner space of the cylinder 6 except that portion of the racks 3|, 32, which reaches to the points where the racks are fastened to the rear faces of the pistons I2. The exhaust ports 29 are provided in the wall of the outer cylinder l, in which are also provided nozzles 40 for delivering fuel to the combustion chamber.

Fig. 5 illustrates an embodiment similar to that shown in Fig. 4. Here the inner cylinder 6 is not stationary but movable and connected to the motor piston 1. The other flying body comprising the motor piston 6, the connecting member I and the compressor piston I2, encloses an inner hollow space 2|, in which the cylinder 6 is guided in a gas-tight manner. The chamber 2| is connected in the same manner as in Fig. 4 to an annular chamber 38, defined by the compressor piston l2 and the partition 36, the chambers 2| and 38 forming a scavenging pump delivering scavenging air to a scavenging air tank 4| surrounding the outer cylinder l and being connected to the combustion chamber by scavenging ports 21. The chamber 31 defined by the motor piston 6 and the partition 36 is connected to the tank 4| by ports 62. The gearing coupling the flying bodies with each other is designed as a screw gearing, the greater part of which is arranged within the inner cylinder 6. The gearing comprises a sleeve 44 having one end supported axially and undisplaceably in a cross member 45, being free to rotate around its axis. The outer ends of the cross member 45 are secured to the wall of the compressor cylinder 2. The connecting member 9 is provided with suitable longitudinal slots, through which the cross member 45 extends, so that it does not impede the free reciprocation of the pistons 1 and |I. The outer surface of the sleeve 44 is formed with a thread of high pitch engaged by a corresponding thread formed on an extension 46 of the left hand flying body. 'Ihe inner surface of sleeve 44 is formed with a thread of equal pitch and opposite direction to that of the outer surface, which is engaged by a threaded spindle 41 secured to the right hand compressor piston I2. Both ying bodies are secured against rotation, that on the left by the cross member 45, that on the right by a square rod i8 secured to the right hand end Wall 5 of the engine and engaginga correspondingly shaped bore 49 formed in the spindle 41. Thus when the flying bodies reciprocate the sleeve 44' will carry out small reciprocatory angular movements without being axially displaced, and the threaded members connected to the flying bodies and engaging the thread of the sleeve will secure an accurately symmetrical reciprocation of the v flying bodies. If desired, the drive of auxiliary devices such as fuel, cooling water or lubricating oil pumps may be derived from the rotating sleeve 44. In the embodiment shown ingFig. the end of the sleeve 44 is provided with a cam 5|, driving the piston of a fuel pump 50 by means of a driving rod 52. The pump 50 delivers fuel to the inlet nozzles 40 through connecting pipes 53 and 54.

In order to cool the inner cylinder 6, an inset member 55 is provided which is secured to the cross member 45 by means of hollow rods 56. The inset member is hollow and arranged to withdraw heat from the cylinder 6. Cooling water is fed through a pipe 51 and through some of the hollow rods 56 and Withdrawn throug the other hollow rods 56 and a pipe 58.

The embodiment shown in Fig. 6 is similar'to that shown in Fig. 5, however, the chamber 2| is designed not as a scavenging pump chamber, but as an energy storing chamber, to which energy is fed during the motor compression stroke, which is re-fed to the iiying bodies during the motor working stroke. The wall I0 of the chamber 2| is provided near its outer end with ports 6|, in which non-return valves 62 are provided, which open only into the chamber 2|. The non-return valves define the amount of initial pressure in the chamber 2| existing before the beginning of the compression and they prevent the withdrawal of compressed air from the chamber 2|.

The gearing for coupling the ying bodies with each other is designed in the embodiment shown in Fig. 6 as a hydraulic gearing, the coupling liquid of the gearing being used as a cooling liquid for the cylinder 6. To this end a casing 64 is arranged within the cylinder 6 which is secured to the left hand end wall 4 of the engine by means of a hollow rod 65. The casing 64 encloses two cylinders 66 and 61 in which pistons 68 and 69 respectively are arranged for reciprocation. Piston 68 is connected to the left hand flying body by means of a rod 1|, piston 69 being connected in asimilar manner to the right hand iiying body by means of a rod 12, the rods 1| and 12 extending through the casing 64 at both end walls thereof in order to obtain equal working surfaces at each side of the pistons 68 and 69. The cylinders 66 and 61 are connected with each other at their ends and are lled with a suitable liquid, so that a displacement of one of the pistons in one direction causes a corresponding displacement of the other piston in opposite direction, thus securing a symmetrical reciprocation of the flying bodies. In order to use the coupling liquid filling the cylinders 66 and 61 as a cooling liquid for the inner cylinder 6, an intermediate chamber 13 packed at its ends is provided between the casing 64 and the cylinder 6, which is connected with the cylinder 61 by a port 14 and to the cylinder 66 by a non-return valve 15. At the left hand ends the cylinders 66 and 61 are connected with each other not directly, but by means of pipes 11 and 18 leading to a re-cooling device 16, the pipe 11 being connected to the cylinder 66 by a non-return valve 19. In consequence thereof during the outward stroke of the ying bodies the piston 68 forces the liquid at the left hand side through the nonreturn valve 15 into the annular chamber 13 and from there through port 14 into the cylinder 61. When owing through the chamber 13 the liquid withdraws heat from the cylinder 6. Dur- 18 into athe re-cooling deyice 16 and from there.

after having been cooled, through pipe 11 back to cylinder 66, whereupon the cycle may be repeated, i. e. the cooling liquid passes from the cylinder 66 through the check valve 15 into the annular space 13 and from here through the opening 14 back into the cylinder space 61. Thus it will be seen that a portion of the coupling liquid is continuously conveyed in a closed circuit through the cooling chamber 13 and the re-cooling device .16.

Figs. 7 and 8 illustrate an embodiment of my invention similar to that shown in Fig. 1. Here additional scavenging ports 21 are provided in the wall of the outer cylinder which connect the combustion chamber With an annular chamber 25' connected to the scavenging pumps by connections 24 and 24. Additional exhaust ports 29 are provided in the wall of the outer cylinder opening into an annular chamber 2B connected to the exhaust pipe 30 by means of a pipe 30.

As will be seen from Fig. 8, the scavenging ports 21 and 21 are inclined with respect to the radial direction in such manner that both the currents of scavenging air entering from the inner chamber 25 and from the outer chamber 25',

respectively, carry out in the combustion chamber circulations of uniform direction (indicated in Fig. 8 by the arrows a and b) which will unite into a single circulating current of scavenging air.

Fig. 9 illustrates an embodiment of the invention somewhat similar to that shown in Fig. 4, however distinguished therefrom by the fact that in Fig. 9 the partitions 36 and consequently also the spaces intermediate the partitions 36 and the rear faces of the motor pistons 1 or 6 are arranged on both sides of the engine. On the right side of the engine the intermediate space 331 acts as a buier space, in which during the motor working stroke energy is stored by the compression of the gas contained in that space, the energy thus stored being again delivered during the return stroke. On the left hand side of the engine the intermediate space |31 acts as a working spaceof anv additional scavenging pump, the air being sucked in through the valves |22 and passing after compression through the valves |23, piping |24 and boring |25'provided in the structural member 34 into the interior of the cylinder 6, into which is passed also the scavenging air supplied from the spaces 2| through the valves 23. All other structural elements correspond to those illustrated and described with reference to Fig. 4 and are therefore provided with the same reference numerals as used in connection with Fig. 4.

Fig. 10 likewise illustrates an embodiment of the invention of a type similar to that shown in Fig. 4, being similarly related to Fig. 9. However Fig. 10 illustrates a two stage compressor, in which the space 31 of Fig. 4 is modified, on both sides of the engine, as a compressor space 231 for the second compressor stage. The structural elements corresponding to those illustated in Fig. l4 have likewise been marked with the reference numerals used in connection with Fig. 4. The embodiment according to Fig. 10 is distinguished from that shown in Fig. 4 quite particularly by the fact, that the pressure gas compressed in the compressor working spaces l5 is not at once supplied to the consumption place, but is passed supplied, through the pressure valves 2 I1 and the pipes 2|8, to the consumption place.

I wish it to be understood 'that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:-

1. A free piston motor compressor comprising two cylinders, one arranged coaxially Within the other, a pair of annular free pistons arranged for reciprocation in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces differing in size and being rigidly spaced from each other more than the length of stroke of each piston, and an energy consumer at either end of the outer cylinder arranged to be acted upon by the rear face of a piston and to consume substantially all the energy generated in said combustion chamber.

2. A free piston motor compressor comprising two cylinders, xed to each other, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocation in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces differing in size and being rigidly spaced from each other more than the length of stroke of each piston, the inner cylinder having a uniform diameter throughout the length of stroke of said pistons," and an energy consumer at either end of the outer cylinder arranged to be acted upon by the rear face of a piston and to consume substantially all the energy generated in said combustion chamber.

3. A free piston motor compressor comprising two cylinders xed to each other, one arranged coaxially within the other, a p air of annular free pistons arranged for reciprocation in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces diiering in size and being rigidly spaced from veach other more than the length of stroke of each piston, the inner cylinder extending substantially along the total stroke of said pistons; supporting means arranged in the axis of said inner cylinder and having a crosssection less than that of said inner cylinder, and an energy consumer at either end of the outer cylinder arranged to be acted upon by the rear face of a piston and to consume substantially all the energy generated in said combustion chamber.

4. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons larranged for reciprocation in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces differing in size and being rigidly spaced from each other more than the length of stroke of each piston, the inner cylinder being connected to one of said pistons, the other piston comprising a ho1low extension, means for guiding said inner cylinder in said extension in a gas-tight manner, and an energy consumer at either end of the outer cylinder arranged to be acted upon by'the rear face of a piston and to consume substantially all the energy generated in said combustion chamber.

5. A free piston motor compressor vcomprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular space formed by said cylinders, a gearing for coupling said pistons with each other, said gearing being at least partly arranged within the inner cylinder, and an energy consumer at either end of the outer cylinder arranged to be acted upon by the rear face of a piston.

6. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, the inner cylinder being connected to one of said pistons, a hollow extension formed on the other piston, means for guiding said inner cylinder in said extension in a gas-tight manner, and gas inlet and exhaust valves associated with said extension.

7. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, the inner cylinder being connected to one of said pistons, a hollow extension formed in the other piston, means for guiding said inner cylinder in said extension in a gas-tight manner, and air inlet and exhaust valves associated with said extension for feeding scavenging air to the engine.

8. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, the inner cylinder being connected to one of said pistons, a hollow extension formed onthe other piston, means for guiding said inner cylinder in said extension in av gas-tight manner, and cooling means for the inner surface of said inner cylinder.

9. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, the inner cylinder being connected to one of said pistons, a hollow extension formed on the other piston, means for guiding said inner cylinder in said extension in a gas-tight manner, a stationary member arranged in said inner cylinder, and common means for cooling said member and said inner cylinder.

A10. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocation in opposite directions in the annular combustion chamber between said cylinders, the inner cylinder being connected to one of said pistons, the other piston comprising a hollow extension, means for guiding said inner cylinder in said extension in a gas-tight manner, a stationary member arranged in said inner cylinder, an hydraulic coupling for said pistons and means for circulating liquid through said stationary member and said coupling.

11. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, the inner cylinder being connected to one of said pistons, a hollow extension formed on the other piston, means for guiding said inner cylinder in said extension in a gas-tight manner, a stationary member Yarranged in said inner cylinder, means for cooling said inner cylinder through said member, an hydraulic cou- 'pling for coupling said pistons with each other,

means for circulating liquid through said stationary member and said-coupling, and means for recooling the circulating liquid.

12. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocation in opposite directions in the annular combustion chamber between said cylinders, a gearing coupling said pistons and comprising an axially immovable member extending into the inner cylinder and an axially fixed rod extending through one of said pistons and supporting said member.

13. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, .a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, a gearing coupling said pistons and comprising an axially immovable member extending into the inner cylinder, and a xed cross member extending radially through longitudinal slots in the side wall of one of said pistons, and supporting said axially immovable member.

14. A free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons held against rotation, but free to reciprocate in opposite directions in the annular combustion chamber between said cylinders, a screw gearing for coupling said pistons extending into the inner cylinder, said gearing comprising an axially arranged sleeve threaded externally and internally in opposite directions and free to rotate but axially immovable, an internally and an externally threaded member, said members being connected to said plstons and engaging the outer and inner threads of said sleeve, respectively.

15. A .free piston motor compressor comprising two cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces differing in size and being rigidly spaced from each other more than the length of stroke of each piston and scavenging ports in the walls of each of said cylinders.

16. A free piston motor compressor comprising two cylinders, one arranged coaxially Within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces differing in size and being rigidly spaced from each other more than the length of stroke of each piston, and scavenging ports in the walls of each 0f said cylinders, all said ports being inclined in the same circumferential direction to the cylinder radii.

17. A free piston motor compressor comprising two coaxially arranged cylinders, one arranged coaxially within the other, a pair of annular free pistons arranged for reciprocaticn in opposite directions in the annular combustion chamber between said cylinders, each piston being formed with a pair of faces diiering in size and being rigidly spaced from eachother more than the length' of stroke of each piston, the inner cylinder 5 being connected to one of said pistons, a. hollow extension formed on the other piston, means for guiding said inner cylinder in said extension in a gas-tight manner, and means enabling said extension to operate as an energy storage chamber.

ing chamber in the middle part and a compressor working chamber at either end of said casing, two freely movable masses arranged in said casing for reciprocation in opposite directions, each movable mass being formed with an annular end 5 face facing said motor working chamber and forming a piston face therein, and with another end face, differing in size, from said annular end face and facing one of said compressor working chambers for operating as a piston face therein. a 10 rigid connecting member between each pair of piston faces, said member being adapted to'space said faces a distance which exceeds the stroke of that freely movable mass, to which the said connectingrnember appertains, an outer and an inner l5 cylindricall wall, said Walls coniining between .them said motor working chamber which is arrangedbetween said annular piston end faces. a gearing connecting said 'freely movable masses 'for synchronous motion in opposite directions. v 20 HERMANN .JNICKE- 

